There is a need for development of sustainable energy sources, and bio ethanol is an attractive source as fuel for transportation. Therefore, there is a need for a process that can produce bio ethanol at a low cost. There is further a need for providing alternative sources of protein for human food and animal feed.
The ability of yeast to convert simple sugars into ethanol is well known. The conversion process is frequently performed by milling a starch-containing raw material and converting the starch into fermentable sugars by enzymatic or acid hydrolysis. After this, yeast is added to ferment the sugars to alcohol and carbon dioxide.
This process is usually performed at low dry matter content in a batch or fed-batch or a continuous process with water content of 90% or more. In 2nd generation production of bio ethanol the dry matter in the fermentation broth is reported to be up to approx. 20%. After fermentation the alcohol is distilled off.
From an economic point of view the high water content in the process is undesirable for the following reasons: High processing costs and high investment costs due to the large volume of the reaction vessels.
WO 2005/069840 A2 discloses a process for producing a fermentation product, such as ethanol, from milled starch-containing material comprising saccharifying the milled starch-containing material with a specially derived glucoamylase without gelatinization of said starch-containing material and fermenting using a fermenting microorganism.
WO 2006/102907 A1 discloses a method of preparing a fermented protein product derived from yeast and proteinaceous pulse parts by fermenting under anaerobic conditions at water content not exceeding 80% and incubating the fermented mixture in a closed system.
WO 2004/113490 A3 discloses a method for the directed, selective solid-phase culturing of stable microbial mixed populations for the continuous preparation of defined enzyme and metabolite mixtures and a suitable bioreactor therefore.
WO2006/129320 A2 discloses a method of producing a protein concentrate from starch containing grain which method comprises fermentation, and wherein the fermentation product can be ethanol.
WO 2006/113683 A2 discloses a method for the production of ethanol and a modified animal feed by saccharification and fermentation.
WO2006/056838 A1 discloses a process for liquefaction and saccharification of polysaccharide containing biomasses having a dry matter content of above 20%, which method comprises enzymatic hydrolysis combined with mixing by a gravity based type of mixing providing mechanical processing. The resulting processed biomass of the process may be further utilized for ethanol production in a subsequent fermentation process.
WO 2007/036795 A1 discloses a process for production of fermentation products, including bioethanol by pretreatment and enzymatic hydrolysis fermentation of waste fractions containing mono- and/or polysaccharides, having a dry matter content of above 20% using free fall mixing for the mechanical processing of the waste fraction and subsequent fermentation.
A fermentor for processing a raw material and an operational method therefore is disclosed in EP 1 355 533 B1; the fermentor disclosed is for continuous processing of a product mixture, particularly dough, or a mixture of water and ground cereal products. A vertical reactor for continuous fermentation utilizing an Archimedean screw is disclosed in GB 2 049 457 A.
The object of the present invention is to provide an improved method for the production of bio ethanol allowing simultaneous production of a valuable fermented, solid product, where the water content during the process is low.
Another object is to provide a process, which can be performed at low costs due to the low water content and equipment of low investment and thereby also provide the products at lower costs.
Yet another object is to provide a fermented, solid product of high commercial value.
These objects are fulfilled with the process and the products of the present invention.